Conventionally, to enhance convenience in using the videophone function, a cellular telephone apparatus is proposed wherein an imaging/display unit constituting a part of the cellular telephone apparatus is provided and is separable from a calling unit constituting the main body of the cellular telephone apparatus (for example, JP 2004-120056). In this cellular telephone apparatus, the imaging/display unit and calling unit are both provided with batteries, and each of the units is thus configured to be able to operate without receiving power supply from the outside.
Meanwhile, cellular telephone apparatuses have currently been installed with various functions, and in the partially separable cellular telephone apparatus as described above, it is considered that the function usable in each unit exists separately (for example, the voice calling function only is present in the calling unit as described above). Then, when such a function is used frequently, an event may occur that the battery of one of the units is exhausted excessively. In this case, it can be considered that some function becomes unavailable with the imaging/display unit connected to the calling unit, etc. and that it is made difficult to ensure the stable operation of the cellular telephone apparatus.